import math

[n, m] = [int(i) for i in raw_input().split(' ')]
f = [int(i) for i in raw_input().split(' ')]

f = sorted(f);
minDist = min([(f[i + n - 1] - f[i]) for i in range(m - n + 1)]) if m > n else f[n - 1] - f[0]
print minDist